Systems and methods for fabricating objects from bulk metallic glass matrix composites using primary crystallization

ABSTRACT

Systems and methods in accordance with embodiments of the invention implement bulk metallic glass matrix composites in the fabrication of objects. In one embodiment, a method of fabricating an object including a bulk metallic glass matrix composite includes: forming a bulk metallic glass matrix composite composition into the shape of the object to be fabricated; and developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions that are softer than the surrounding matrix as measured by one of: the shear modulus, the elastic limit, and the hardness; where the bulk metallic glass matrix composite composition is such that the extent of the presence of the inclusions can be made to vary.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application claims priority to U.S. Provisional Application No. 61/763,292, filed Feb. 11, 2013, the disclosure of which is incorporated herein by reference.

STATEMENT OF FEDERAL FUNDING

The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. 202) in which the Contractor has elected to retain title.

FIELD OF THE INVENTION

The present invention generally relates to fabricating objects from bulk metallic glass matrix composites.

BACKGROUND

Metallic glasses, also known as amorphous alloys, embody a relatively new class of materials that is receiving much interest from the engineering and design communities. Metallic glasses are characterized by their disordered atomic-scale structure in spite of their metallic constituent elements—i.e. whereas conventional metallic materials typically possess a highly ordered atomic structure, metallic glass materials are characterized by their disordered atomic structure. Notably, metallic glasses typically possess a number of useful material properties that can allow them to be implemented as highly effective engineering materials. For example, metallic glasses are generally much harder than conventional metals, and are generally tougher than ceramic materials. They are also relatively corrosion resistant, and, unlike conventional glass, they can have good electrical conductivity. Importantly, the manufacture of metallic glass materials lends itself to relatively easy processing. For example, the manufacture of a metallic glass can be compatible with an injection molding process.

Nonetheless, the manufacture of metallic glasses presents challenges that limit their viability as engineering materials. In particular, metallic glasses are typically formed by raising a metallic alloy above its melting temperature, and rapidly cooling the melt to solidify it in a way such that its crystallization is avoided, thereby forming the metallic glass. The first metallic glasses required extraordinary cooling rates, e.g. on the order of 10⁶ K/s, and were thereby limited in the thickness with which they could be formed. Indeed, because of this limitation in thickness, metallic glasses were initially limited to applications that involved coatings. Since then, however, particular alloy compositions that are more resistant to crystallization have been developed, which can thereby form metallic glasses at much lower cooling rates, and can therefore be made to be much thicker (e.g. greater than 1 mm). These thicker metallic glasses are known as ‘bulk metallic glasses’ (“BMGs”).

In addition to the development of BMGs, ‘bulk metallic glass matrix composites’ (BMGMCs) have also been developed. BMGMCs are characterized in that they possess the amorphous structure of BMGs, but they also include crystalline phases of material within the matrix of amorphous structure. For example, the crystalline phases can exist in the form of dendrites. The crystalline phase inclusions can impart a host of favorable materials properties on the bulk material. For example, the crystalline phases can allow the material to have enhanced ductility, compared to where the material is entirely constituted of the amorphous structure.

SUMMARY OF THE INVENTION

Systems and methods in accordance with embodiments of the invention implement bulk metallic glass matrix composites in the fabrication of objects. In one embodiment, a method of fabricating an object including a bulk metallic glass matrix composite includes: forming a bulk metallic glass matrix composite composition into the shape of the object to be fabricated; and developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions that are softer than the surrounding matrix as measured by one of: the shear modulus, the elastic limit, and the hardness; where the bulk metallic glass matrix composite composition is such that the extent of the presence of the inclusions can be made to vary.

In another embodiment, the forming of the bulk metallic glass matrix composite composition is achieved using one of: a thermoplastic forming technique and a casting technique.

In yet another embodiment, the forming of the bulk metallic glass matrix composite composition is achieved using one of: die casting, injection casting, rapid capacitive discharge forming, powder injection metallurgy, and investment casting.

In still another embodiment, the non-equilibrium inclusions are developed such that they impart desired materials properties in the object to be fabricated.

In still yet another embodiment, developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions includes subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate.

In a further embodiment, subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate develops non-equilibrium inclusions in a first region of the object to be fabricated, but not in a second region of the object to be fabricated.

In a still further embodiment, the second region of the object to be fabricated is locally heat treated to develop non-equilibrium inclusions.

In a yet further embodiment, developing the bulk metallic glass matrix composite includes heat treating the formed bulk metallic glass matrix composite composition.

In a still yet further embodiment, the heat treating is annealing.

In another embodiment, the heat treating is localized to regions of the formed bulk metallic glass matrix composite composition.

In still another embodiment, the extent of the presence of the inclusions can be made to vary by thermal processing.

In yet another embodiment, the crystalline structures that are developed undergo martensitic transformation when subjected to strain beyond a predetermined threshold.

In still yet another embodiment, the bulk metallic glass matrix composite composition does not include beryllium.

In a further embodiment, the bulk metallic glass matrix composite composition is Zr₄₈Cu_(47.5)Al₄CO_(0.5).

In a still further embodiment, the non-equilibrium inclusions are B2 phase inclusions.

In a yet further embodiment, the bulk metallic glass matrix composite composition is Cu_(47.5)Zr_(47.5)Al₅.

In a still yet further embodiment, the bulk metallic glass matrix composite composition is one of: a CuZr-based composition, a TiCu-based composition, an NiTi-based composition, a CuZnAl-based composition, an FeNi-based composition, NiP-based composition, FeP-based composition, a FeNiCoAlTaB-based composition, a ZrTi-based composition, a ZrNb-based composition, an NiNb-based composition, a ZrV-based composition, a TiNB-based composition, a ZrTiTa-based composition, TiV-based composition, TiTa-based composition, a ZrTa-based composition, and a ZrCu based composition.

In another embodiment, the non-equilibrium inclusions are spherical.

In yet another embodiment, the object to be formed is a golf head casing.

In still another embodiment, a striking surface of the golf head casing is locally heat treated to develop the non-equilibrium inclusions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of fabricating an object from a bulk metallic glass matrix composite in accordance with embodiments of the invention.

FIG. 2 illustrates the materials properties for a Zr₄₈Cu_(47.5)Al₄Co_(0.5) BMGMC composition that can be implemented in the manufacture of an object in accordance with embodiments of the invention.

FIGS. 3A-3B illustrates the enhanced ductility that a CuZrAlCo BMGMC can be made to possess and the martensitic transformation that can allow it to accommodate strain, and thereby be used in the fabrication of an object in accordance with embodiments of the invention.

FIG. 4 illustrates how the materials properties of a Cu₄₇₅Zr₄₇₅Al₅ BMGMC can be made to vary by controlling the volume fraction of the B2 phase, and how the alloy can thereby be implemented in the fabrication of an object in accordance with embodiments of the invention.

FIG. 5 illustrates alloying a BMGMC composition so that it be formed into the shape of an object to be fabricated and include a desired microstructure in accordance with embodiments of the invention.

FIG. 6 illustrates annealing a BMGMC to develop non-equilibrium crystalline inclusions in accordance with embodiments of the invention.

FIG. 7 illustrates applying a localized heat treatment to locally develop a microstructure in an object to be fabricated in accordance with embodiments of the invention.

FIGS. 8A-8B illustrate a golf club head casing and an electronic casing that can be heat treated locally to develop their respective microstructures in accordance with embodiments of the invention.

FIG. 9 illustrates developing a BMGMC composition to be used in the formation of a wedge-shaped object in accordance with embodiments of the invention.

FIGS. 10A-10D illustrate that the volume fraction of a B2 phase within a Zr₄₈Cu_(47.5)Al₄Co_(0.5) can vary based on thickness of the geometry being cooled, and that this phenomenon can be accounted for in accordance with embodiments of the invention.

FIGS. 11A-11B illustrate DSC curves and XRD scans that further demonstrate that the volume fraction of the B2 phase of a Zr₄₈Cu_(47.5)Al₄CO_(0.5) composition is a function of the geometry of the object being cooled, and that this phenomenon can be accounted for in accordance with embodiments of the invention.

DETAILED DESCRIPTION

Turning now to the drawings, systems and methods for implementing bulk metallic glass matrix composites in the fabrication of objects are illustrated. In many embodiments, a bulk metallic glass matrix composite composition is formed into the shape of an object to be fabricated, and the composition is developed to include non-equilibrium inclusions that are softer than the surrounding matrix (e.g. as measured by shear modulus, elastic limit, or hardness). In a number of embodiments, the formed composition is heat treated to develop the inclusions. In several embodiments, the heat treating is localized to regions where it is desired that the object be especially robust.

Although bulk metallic glasses can possess a number of advantageous materials properties that might make them suitable materials from which to fabricate some structural components from, they might not have the requisite resistance to brittle fracture and/or ductility that can allow them to implemented in many applications where a more robust material is desirable. Thus, bulk metallic glass matrix composites have been studied for their viability in applications where a more robust material would be desirable. As discussed above, BMGMCs are characterized by their crystalline inclusions that can enhance the robustness of the underlying BMG material. For example, a BMGMC can have enhanced fracture toughness, fatigue endurance, and tensile ductility compared to a base BMG. Generally, the crystalline inclusions can be understood to accommodate applied strain through, e.g. shear band arrest, martensitic transformation, twinning, etc., and thereby cause the observed enhanced materials properties. Further, it is generally understood that in order for a BMGMC to have enhanced materials properties relative to the underlying BMG, the crystalline inclusions should be soft and course.

Zr—Ti—Be BMGMC materials are an example of BMGMCs that can be made to have favorable materials properties. Zr—Ti—Be BMGMC materials typically include elastic and soft body-centered cubic crystalline dendrites. Some Zr—Ti—Be BMGMC systems are particularly distinct in that they can demonstrate tensile ductility above 1 GPa of yield stress. Nonetheless, in spite of their potentially favorable materials profile, this alloy system has some limitations that may limit its viability as an engineering material. For example, in many applications it is desirable to implement a material that is free of beryllium. Furthermore, in many Zr—Ti—Be systems, the crystalline inclusions are equilibrium phase inclusions, and as a result, the extent of the presence of the crystalline inclusions (e.g. as measured by volume fraction) is generally independent of the cooling rate (or other thermal processing) by which the BMGMC is formed. Instead, the cooling rate (or other thermal processing) impacts the overall morphology of the dendritic structures—for example, a slower cooling rate may cause a course dendritic microstructure to develop, whereas a more rapid cooling rate can cause a finer dendritic microstructure to develop. Importantly, in order to obtain a more advantageous materials profile for these systems, the dendritic structures typically must be developed to be of certain coarseness. Recall that when BMGMCs are formed into objects, they are typically heated so that they can be formed, thereafter formed into the desired shape, and subsequently cooled—the cooling rate of the BMGMC is largely a function of the geometry of the shape to be formed, e.g. a thicker geometry will cool more slowly than a thinner one. Thus, when a geometry includes varying thicknesses, the cooling rate throughout the part may be uneven—thicker portions of the geometry may cool more slowly than thinner portions. As a result, when a Zr—Ti—Be BMGMC is implemented, the microstructure can vary throughout the geometry, and the desired microstructure may appear only for a region of the geometry, whether or not it is even desired for that region of the geometry. In many instances it may be desirable for other areas of the object having such a geometry to contain the crystalline inclusions that bolster the materials properties. In general, it may be desirable to be able to more precisely control the microstructure, and thereby the materials properties, throughout the geometry.

Accordingly, in many embodiments, methods of fabricating objects are implemented that allow a more precise control of the development of the resulting microstructure, which impacts the overall material properties. For example, in many embodiments, BMGMC compositions that can be made to develop non-equilibrium phase crystalline inclusions are implemented in the fabrication of objects. The non-equilibrium phase inclusions are such that the extent of their presence (e.g. as measured by their volume fraction) can be controlled using thermal processing methods (e.g. cooling rate and annealing). In some embodiments, crystalline phases are implemented that result from primary crystallization due relatively slower cooling rate (e.g. a cooling rate slower than that required to form a monolithic glass). Additionally, in many instances the crystalline inclusions are softer than the surrounding amorphous matrix. For example, the shear modulus, the elastic limit, and/or the hardness of the crystalline inclusions can be less than that of the surrounding amorphous matrix. In this way, the BMGMC composition can be thermally processed to more precisely control the resulting microstructure, and thereby more precisely influence the materials properties. These processes are discussed in greater detail below.

Fabricating Objects from BMGMC Materials

In many embodiments, methods for fabricating objects from bulk metallic glass composite matrix materials that include non-equilibrium phase inclusions are implemented. Any suitable object may be fabricated, including objects that have geometries with varying thicknesses. For example, the casing of a golf club head can be fabricated from a BMGMC. As mentioned above, BMGMC materials can provide for a more robust materials.

A process for fabricating an object from a BMGMC using a casting technique or a thermoplastic forming technique is illustrated in FIG. 1. In particular, the process 100 includes forming 110 a BMGMC composition into the shape of the object to be fabricated using a casting technique or a thermoplastic forming technique. Again, any suitable object having any suitable shape can be fabricated, including objects having varying thicknesses. The BMGMC composition is one that can be made to form non-equilibrium crystalline inclusions using thermal processing techniques such as a rapid cooling rate or annealing. The non-equilibrium crystalline inclusions are metastable, and can be achieved, for example, by rapidly cooling the composition. Importantly, the extent of their presence (e.g. as measured by volume fraction) can be controlled by thermal processing techniques. For example, a slower cooling rate can promote their development. Similarly, annealing the composition can also promote the growth of the inclusions.

Zr₄₈Cu_(47.5)Al₄Co_(0.5) is one example of a bulk metallic glass matrix composite composition that can be implemented in accordance with embodiments of the invention. This alloy can be made to form B2 phase non-equilibrium nanocrystals; it is generally understood that the B2 phase nanocrystals can accommodate strain that the bulk material is being subjected to by undergoing a martensitic transformation. In this way, the B2 phase nanocrystals can endow the bulk material with enhanced material properties. Importantly, the extent of the presence of the B2 phase can be made to vary using thermal processing techniques. For example, a formed Zr₄₈Cu_(47.5)Al₄Co_(0.5) BMGMC material can be annealed to promote the development of the B2 phase. Generally, the materials properties of the bulk material can be approximated by the rule of mixtures, e.g. the greater the presence of the B2 phase nanocrystals, the more the bulk material will conform to the materials properties of the B2 phase nanocrystals. Conversely, the greater the presence of the amorphous matrix, the more the bulk material will conform to the properties of the amorphous matrix. This approximation is generally valid until the B2 crystalline phase exceeds a volume fraction of approximately 30%.

FIG. 2 illustrates a stress-strain plot of a Zr₄₈Cu₄₇₅Al₄Co_(0.5) BMGMC material relative to that of a Zr_(39.6)Ti_(33.9)Nb_(7.6)Cu_(6.4)Be_(12.5) material—note that the Zr₄₈Cu₄₇₅Al₄CO_(0.5) material include B2 phase material that undergo work-hardening in tension from martensitic transformation, which results in a more robust alloy. In stark contrast, the Zr_(39.6)Ti_(33.9)Nb₇₆Cu₆₄Be_(12.5) material experiences necking. The respective microstructures are also depicted, and it is seen that a crack is able to propagate through the Zr_(39.6)Ti_(33.9)Nb₇₆Cu₆₄Be_(12.5) material. Interestingly, the B2 crystalline inclusions precipitate polymorphically. For both depicted materials, the shear moduli of the crystalline inclusions are less than that of the respective amorphous matrices. Note that Zr₄₈Cu_(47.5)Al₄Co_(0.5) BMGMC materials can demonstrate up to approximately 10% total strain in tension, and can have a glass forming ability such that an approximately 5 mm thick part can be cast fully amorphous. FIG. 2 is reproduced from D.C. Hofmann, Science 329, 1294 (2010), the disclosure of which is hereby incorporated by reference.

FIG. 3A depicts that ZrCuAlCo systems can demonstrate extensive ductility. The microstructure is also depicted and again demonstrates B2 phase crystalline material. FIG. 3B illustrates that for such systems, strain is accommodated through martensitic transformation. Specifically, it is illustrated that the martensitic transformation greatly hardens the crystalline material. FIGS. 3A and 3B are reproduced from Y. Wu et al., Adv. Mater. (Deerfield Beach Fla.) 22, 2270 (2010), the disclosure of which is hereby incorporated by reference.

FIG. 4 depicts stress-strain curves for an alternate CuZrAl system—Cu_(47.5)Zr_(47.5)Al₅—that can be made to include B2 phase non-equilibrium crystalline inclusions in accordance with embodiments of the invention. In particular, stress-strain curves are shown for the varying volume fractions of the B2 phase non-equilibrium crystalline inclusions. The varying volume fractions were obtained by annealing the material. In essence, it is illustrated that the materials properties of the BMGMC system can be made to vary by varying the volume fraction of the B2 phase non-equilibrium crystalline inclusions. Table 1 below depicts the materials properties of the crystalline inclusions relative to those of the amorphous matrix. Importantly, the shear modulus of the B2 phase is less than that of the amorphous matrix.

TABLE 1 Elastic Properties of B2 CuZr and the glassy phase in Cu_(47.5)Zr_(47.5)Al₅ E G B Phase (GPa) ν (GPa) (GPa) B2 CuZr 82 ± 2 0.385 ± 0.004 29 ± 1 118 ± 3 Glass 89 ± 2 0.373 ± 0.003 33 ± 2 117 ± 3

FIG. 4 and Table 1 are obtained from S. Pauly et al., Appl. Phy. Lett. 95, 101906 (2009), the disclosure of which is hereby incorporated by reference.

Bear in mind that although the development of B2 crystalline phases has been discussed in conjunction with a ZrCuAlCo system, B2 crystalline phases can also develop in other systems-for example TiCu alloys can develop a B2 phase. Furthermore, any BMGMC composition that can be made to form any non-equilibrium crystalline phase—not just a B2 phase—can be implemented in accordance with embodiments of the invention. Generally, any BMGMC composition that can be made to include non-equilibrium crystalline inclusions, including any of the systems discussed above, can be implemented in accordance with embodiments of the invention. For example, the BMG composition can be one of: a CuZr-based composition, a TiCu-based composition, an NiTi-based composition, a CuZnAl-based composition, an FeNi-based composition, NiP-based composition, FeP-based composition, a FeNiCoAlTaB-based composition, a ZrTi-based composition, a ZrNb-based composition, an NiNb-based composition, a ZrV-based composition, a TiNB-based composition, a ZrTiTa-based composition, TiV-based composition, TiTa-based composition, a ZrTa-based composition, and a ZrCu based composition. When a composition is referred to as being based on an element or set of elements, it is meant that those elements are present in the most amounts.

Referring back to FIG. 1, note that the BMGMC composition can be formed into the shape of the object to be fabricated using any casting technique or any thermoplastic forming technique. For instance, the forming technique can be one of: die casting, injection casting, rapid capacitive discharge forming, powder injection metallurgy, or investment casting. Indeed, any forming technique can be implemented in accordance with embodiments of the invention.

The process 100 further includes developing 120 the BMGMC composition to include non-equilibrium inclusions that have a shear modulus less than that of the surrounding amorphous matrix. For example, in some embodiments, the forming of the BMGMC composition into the shape of the object to be formed inherently causes the development of the non-equilibrium inclusions. In some embodiments, a base BMGMC composition is alloyed such that the formation of the BMGMC composition inherently results in the development of the non-equilibrium inclusions. FIG. 5 illustrates the process of alloying a BMGMC so that the formation of the BMGMC composition inherently results in the development of the desired microstructure. In particular, a mold 502 in the shape of the object to be fabricated is illustrated, and the BMGMC composition is meant to be cast into the mold thereby forming it in the shape of the object to be fabricated. When a base BMGMC composition 504 is cast into the mold, the cooling rate of the BMGMC composition (which is a function of the geometry of the object to be formed), does not facilitate the development of the desired microstructure; instead the cast microstructure is over-extensively crystalline. Accordingly, this BMGMC composition 504 can be alloyed to improve its glass forming ability so that the cooling rate will instead allow the development of the desired microstructure 506. In this way, BMGMC compositions can be tuned by alloying to achieve a desired microstructure for a given cooling rate. In general, in many embodiments of the invention, the glass forming ability of a BMGMC composition is enhanced, e.g. via alloying, so that thicker geometries of BMGMCs having robust materials properties can be fabricated.

Note that the critical cooling rate to form a monolithic bulk metallic glass can be modeled by:

$R_{c} = \frac{\frac{\pi^{2}k}{L^{2}}\left( {T_{l} - T_{g}} \right)}{\ln \left( {\frac{4}{\pi}\frac{T_{l} - T_{r}}{T_{g} - T_{r}}} \right)}$

This equation indicates that the critical cooling rate to form a glass is a function of only the liquidus temperature, the glass transition temperature, the thermal diffusivity and the length. Glass forming ability can be defined as critical casting thickness, the critical length, Lc, where the centerline can be cooled to below Tg at the critical cooling rate. Thus, the critical casting thickness of a metallic glass can be modeled by:

$L_{c} = \sqrt{\frac{\pi^{2}{k\left( {T_{l} - T_{g}} \right)}}{R_{c}{\ln \left( {\frac{4}{\pi}\frac{T_{l} - T_{r}}{T_{g} - T_{r}}} \right)}}}$

If the object to be fabricated is cooled slower than the critical cooling rate or the object to be fabricated is thicker than the critical casting length, it will begin to crystallize. These principles can be utilized in implementing BMGMC compositions so that desired microstructures can be made to develop.

In some embodiments, developing 120 the BMGMC composition includes annealing the BMGMC composition until the desired microstructure is attained. FIG. 6 illustrates annealing a BMGMC composition until a desired microstructure attained. In particular, a BMGMC composition, as formed 602, is in a fully amorphous state, an annealing step is used to grow a microstructure that includes non-equilibrium crystalline inclusions 604. If desired, another annealing step can be implemented to further grow the crystalline inclusions until the desired microstructure is achieved 606. These processes are particularly effective when the annealing causes the growth of soft non-equilibrium phase crystalline inclusions, and does not correspondingly cause the growth of any hard phases. Note that annealing can be used to grow new inclusions, are alternatively promote the growth of existing inclusions.

Importantly, the described heat-treating processes can be applied in localized regions of the object to be fabricated in accordance with embodiments of the invention. For instance, in many embodiments, a BMGMC composition is formed into an object to be fabricated, and a heat treatment is locally applied to locally develop the microstructure. In this way, particular regions of the object to be fabricated can be developed to be more robust. FIG. 7 illustrates locally developing a BMGMC composition so that it includes non-equilibrium phase inclusions in accordance with embodiments of the invention. In particular, a mold 702 is illustrated, and a BMGMC composition is cast in to the mold so that an amorphous matrix 704 is produced. Subsequently, a heating apparatus 708 can be used to locally heat treat regions of the object to be formed to develop the desired microstructure. In this way, regions of the object to be formed that are expected to experience high stress can be developed to be more robust so they can withstand the expected high stress.

FIGS. 8A and 8B illustrate examples of applications where localized heat treating can be implemented in accordance with embodiments of the invention. In particular, FIG. 8A depicts a golf head casing. In the illustration, the golf head casing is depicted as being cracked at its striking surface. Accordingly, in accordance with embodiments of the invention, such cracking can be avoided by locally heat treating a golf head casing formed from a BMGMC composition so as to develop the microstructure that can allow it is more robust and can withstand striking a golf ball. Similarly, FIG. 8B depicts an electronic casing that may be prone to particular regions of high stress. These particular regions of high stress should be heat treated to develop the microstructure to enable the casing to tolerate the high stress at those particular regions.

Note that the described development 120 of non-equilibrium phase crystalline inclusions can be achieved in any suitable manner in accordance with embodiments of the invention. In many embodiments, the development is achieved using thermal processing, e.g. cooling rates and annealing stages. Additionally, as mentioned previously, the materials properties of the material can in some respects be approximated by the rule of mixtures. Thus, for example, where it is desired that the bulk material adopt a materials profile that is more akin to the crystalline structure, the microstructure can be developed accordingly. Conversely, where it is desired that the bulk material adopt a materials profile that is more akin to the amorphous structure, the microstructure can be developed accordingly. In this way, thermal processing can be used to tune the materials properties, either globally or locally.

Of course, it should be understood that the above mentioned concepts can be implemented in aggregate. For example, FIG. 9 illustrates the fabrication of a wedge-shaped object from a BMGMC material in accordance with embodiments of the invention. In particular, a first attempt to form a BMGMC composition into the wedge shaped object 902 is illustrated. Specifically, a CuZrAl BMGMC material is cast into the wedge shape; however, the forming resulted in excessive crystallization at the thicker part of the wedge. In essence, the cooling rate was not sufficiently high to form the desirable microstructure at the thicker part of the wedge. Accordingly, a second attempt 804 is illustrated whereby a CuZrAl material is alloyed with cobalt to improve its glass forming ability. In the second attempt, the crystalline phases are still excessive in the thicker part of the wedge shaped object, but not as excessive as in the first attempt 902. A third attempt 906 is illustrated whereby the CuZrAl material is alloyed with other elements to further improve its glass forming ability. Any suitable elements can be used to alloy the material to improve its glass forming ability. For example the alloying elements can be selected in view of the following table, which expresses various compositions and how they are impacted by different constituent elements. Note that the materials are designated as amorphous (A), nanocrystalline (X), or composite (C). Additionally, bear in mind that the materials properties were obtained for cylinders of 25 mm diameter and 3 mm thickness. The data in table 2 was measured by the inventor.

TABLE 2 Materials Properties for BMG and BMGMC compositions Est. Density Poisson A/X/C Density (g/cm³) 2.0 Hv E (GPa) K (GPa) G(GPa) G/K Ratio (CuZr)Al7Be10Nb3 A 6.773 6.948 626.5 108.5 119.5 40.2 0.336 0.35 (CuZr)Al5Y2Nb3 A 7.051 6.925 407.4 76.9 110.7 27.8 0.251 0.38 (CuZr)Al7Be5Nb3 A 6.922 7.020 544.4 97.8 118.5 35.9 0.303 0.36 (CuZr)Al7Be7Nb3 A 6.867 6.867 523.9 102.0 115.2 37.7 0.327 0.35 (CuZr)Al7Be7Cr3 A 6.813 6.813 575.1 106.5 116.1 39.5 0.341 0.35 (CuZr)Al5Ni3Be4 A 7.014 7.014 504.3 95.5 115.7 35.1 0.303 0.36 (CuZr)Al7 X 7.007 7.007 510.5 101.4 113.0 37.5 0.332 0.35 (CuZr)Al7Ag7 C 7.224 7.224 496.1 90.6 117.6 33.0 0.281 0.37 (CuZr)Al7Be10 A 6.722 6.722 557.6 104.5 113.9 38.8 0.341 0.35 (CuZr)Al7Be5 A 6.869 6.978 514.3 99.0 114.0 36.5 0.321 0.36 (CuZr)Al7Be7 A 6.811 6.811 550.3 99.0 111.3 36.6 0.329 0.35 (CuZr)Al7Ni5 X 7.052 7.052 570.0 99.2 114.8 36.6 0.318 0.36 Cu40Zr40Al10Be10 A 6.582 6.582 604.3 114.2 117.0 42.7 0.365 0.34 Cu41Zr40Al7Be7Co5 C 6.864 6.864 589.9 103.5 116.8 38.3 0.328 0.35 Cu42Zr41Al7Be7Co3 A 6.846 6.846 532.4 101.3 117.8 37.3 0.317 0.36 Cu47.5Zr48Al4Co0.5 X 7.138 7.138 381.9 79.6 116.3 28.7 0.247 0.39 Cu47Zr46Al5Y2 A 7.003 7.003 409.8 75.3 115.9 27.1 0.233 0.39 Cu50Zr50 X 7.313 7.313 325.9 81.3 116.8 29.4 0.252 0.38

In the third attempt 906, the optimal microstructure is achieved at the thickest part of the wedge-shaped object. Note that the bottom half of the wedge shaped object is entirely amorphous. If it is desired that this portion of the wedge-shaped object be developed to include crystalline phases, this portion of the object can be locally heat treated in accordance with the above-discussion. In this way, an object having varying thickness can be fabricated to include a desirable microstructure throughout its geometry.

That the geometry of the object to be fabricated can impact the cooling rate, which in turn can impact the microstructure is further expressed in FIGS. 10A-10D. In particular, FIGS. 10A-10D depict the microstructures of Zr₄₈Cu_(47.5)Al₄Co_(0.5) BMGMC plate materials having varying thicknesses that were cooled. Specifically, FIG. 10A depicts the microstructure for the BMGMC when it is cooled in the form of a 1×5×30 mm plate; FIG. 10B depicts the microstructure for the BMGMC when it is cooled in the form of a 2×5×30 mm plate; FIG. 10C depicts another view of the microstructure for the BMGMC when it is cooled in the form of a 2×5×30 mm plate; and FIG. 10D depicts a view of the microstructure of a BMGMC when it is cooled in the form of a 3×5×30 mm plate. Note that the presence of the B2 phase gradually increases with the thicker plates. This is because the thicker plates cannot be cooled as rapidly as the thinner cooling rates, and the relatively slow cooling rates precipitate crystalline inclusions. The table below illustrates the materials properties for Zr₄₈Cu_(47.5)Al₄Co_(0.5) BMGMC plate materials. FIGS. 10A-10D and Table 3 are reproduced from H. Kozachkov et al., Intermetallics 39 (2013), pgs. 89-93, the disclosure of which is hereby incorporated by reference.

TABLE 3 Materials Properties for Zr₄₈Cu_(47.5)Al₄Co_(0.5) as a function of Plate Thickness Plate Size (mm) G (Gpa) E (GPa) B (GPa) ν ρ (g/cm³) 0.5 × 5 × 30   32.5 90.1 133 0.387 7.14 1 × 5 × 30 32.9 91.1 133 0.385 7.14 2 × 5 × 30 31.6 87.0 117 0.376 7.14 3 × 5 × 30 31.8 87.6 118 0.376 7.14 ingot 30.4 84.1 120 0.383 7.14

Similarly, FIGS. 11A and 11B depict DSC curves and XRD scans further demonstrating that the presence of crystalline inclusions decreases with the decreasing thickness of a Zr₄₈Cu_(47.5)Al₄Co_(0.5). Specifically, FIG. 11A depicts DSC curves showing that the volume fraction of the B2 phase decreases with the diameter of a cooled rod. Thus, a 1 mm rod of Zr₄₈Cu_(47.5)Al₄Co_(0.5) is largely monolithic, whereas a 5 mm rod includes 70% B2 phase. Similarly, FIG. 11B shows XRD scans from three rods again depicting a similar trend: an increase in the volume fraction of the B2 phase with increasing diameter. FIGS. 11A and 11B are reproduced from H. Kozachkov et al., Intermetallics 39 (2013), pgs. 89-93, the disclosure of which was incorporated by reference above.

Referring back to FIG. 1, the process can further include performing 130 any post-forming operations if desired. For example, the formed part can be machined to install any intricacies.

As can be inferred from the above discussion, the above-mentioned concepts can be implemented in a variety of arrangements in accordance with embodiments of the invention. Accordingly, although the present invention has been described in certain specific aspects, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that the present invention may be practiced otherwise than specifically described. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive. 

What is claimed is:
 1. A method of fabricating an object including a bulk metallic glass matrix composite comprising: forming a bulk metallic glass matrix composite composition into the shape of the object to be fabricated; and developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions that are softer than the surrounding matrix as measured by one of: the shear modulus, the elastic limit, and the hardness; wherein the bulk metallic glass matrix composite composition is such that the extent of the presence of the inclusions can be made to vary.
 2. The method of claim 1, wherein the forming of the bulk metallic glass matrix composite composition is achieved using one of: a thermoplastic forming technique and a casting technique.
 3. The method of claim 2 wherein the forming of the bulk metallic glass matrix composite composition is achieved using one of: die casting, injection casting, rapid capacitive discharge forming, powder injection metallurgy, and investment casting.
 4. The method of claim 2, wherein the non-equilibrium inclusions are developed such that they impart desired materials properties in the object to be fabricated.
 5. The method of claim 4, wherein developing the bulk metallic glass matrix composite composition to include non-equilibrium inclusions comprises subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate.
 6. The method of claim 5, wherein subjecting the bulk metallic glass matrix composite composition to an appropriate cooling rate develops non-equilibrium inclusions in a first region of the object to be fabricated, but not in a second region of the object to be fabricated.
 7. The method of claim 6, wherein the second region of the object to be fabricated is locally heat treated to develop non-equilibrium inclusions.
 8. The method of claim 4, wherein developing the bulk metallic glass matrix composite comprises heat treating the formed bulk metallic glass matrix composite composition.
 9. The method of claim 8, wherein the heat treating is annealing.
 10. The method of claim 8, wherein the heat treating is localized to regions of the formed bulk metallic glass matrix composite composition.
 11. The method of claim 4, wherein the extent of the presence of the inclusions can be made to vary by thermal processing.
 12. The method of claim 4, wherein the crystalline structures that are developed undergo martensitic transformation when subjected to strain beyond a predetermined threshold.
 13. The method of claim 4, wherein the bulk metallic glass matrix composite composition does not include beryllium.
 14. The method of claim 4, wherein the bulk metallic glass matrix composite composition is Zr₄₈Cu_(47.5)Al₄CO_(0.5).
 15. The method of claim 4, wherein the non-equilibrium inclusions are B2 phase inclusions.
 16. The method of claim 4, wherein, the bulk metallic glass matrix composite composition is Cu_(47.5)Zr_(47.5)Al₅.
 17. The method of claim 4, wherein the bulk metallic glass matrix composite composition is one of: a CuZr-based composition, a TiCu-based composition, an NiTi-based composition, a CuZnAl-based composition, an FeNi-based composition, NiP-based composition, FeP-based composition, a FeNiCoAlTaB-based composition, a ZrTi-based composition, a ZrNb-based composition, an NiNb-based composition, a ZrV-based composition, a TiNB-based composition, a ZrTiTa-based composition, TiV-based composition, TiTa-based composition, a ZrTa-based composition, and a ZrCu based composition.
 18. The method of claim 4, wherein the non-equilibrium inclusions are spherical.
 19. The method of claim 4, wherein the object to be formed is a golf head casing.
 20. The method of claim 19, wherein a striking surface of the golf head casing is locally heat treated to develop the non-equilibrium inclusions. 